Tracker to update how we handle the inputs_embeds input, especially in generate, and how we test it.

More precisely:

• Remove support of inputs_embeds in generate in models that don't actually support it. (Check skipped tests)
• Remove as many skips as possible in tests like test_inputs_embeds_matches_input_ids_with_generate or test_inputs_embeds (Check the tests folder and search for inputs_embeds)